1. Field of The Invention
The invention relates to new imidazole derivatives of the formula: ##STR3## wherein R.sub.1 is an (R)- or (S)-1-phenylalkyl group, an (R)- or (S)-1-alkoxycarbonyl-1-phenylmethyl group or an (R)- or (S)-1-aryloxycarbonyl-1-phenylmethyl group, R.sub.2 is hydrogen, a substituted or unsubstituted alkanoyl group, a substituted or an ubsubstituted benzoyl group, a substituted or an unsubstituted benzyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxyalkyl group, a pyranyl group, a substituted or an unsubstituted benzenesulfonyl group, an alkylsulfonyl group, a diarylphosphinyl group, a dialkoxyphosphinyl group or a trialkylsilyl group, and A is a sulfur or oxygen atom. These compounds are suitable as intermediate products for the production of (+) biotin.
2. Background Art
A process is known from U.S. Pat. No. 2,489,232 according to which racemic biotin is produced. But since, as is known, only the optically active (+) biotin is biologically active; the thus-produced racemic biotin must then still be separated into the optical enantiomers. On the one hand, in such a case all reaction steps are performed with racemic materials, as a result of which the doubled amounts of substance must be processed. On the other hand, resolution of the racemic biotin into the corresponding enantiomers is a very complicated process, which in addition is also unprofitable, since the undesirable enantiomer practically no longer racemizes and can no longer be fed back into the process.
An improvement of such process is known from U.S. Pat. No. 2,489,235. In such improvement, the resolution of the racemates is already performed in an earlier step, but still such process has the drawback that most of the reaction steps are performed with racemic material and here too the undesirable enantiomer practically no longer racemizes and can no longer be fed back to the process.
M. Murakami et al. developed an improved process for the production of dl-biotin (cf. Japanese Published Patent Document 31669/1970, 37775/1970, 37776/1970 and 3580/1971). The improvement consists in introducing a carboxybutyl group in the 4-position of the dl-1,3-dibenzylhexahydrothioeno-[3,4-d]-imidazole-2,4-dione. Such dione is reacted with a 1,4-dihalomagnesium butane and then carboxylated with carbon dioxide.
Gerecke et al., German Published Patent Document No. 2058248, have developed a further improvement, by already producing--in an earlier step by the optical resolution of a triethylamine salt of the following formula, in which R is a cholesteryl radical, or of an ephedrine salt of the following formula, in which R is a cyclohexyl radical: ##STR4## and by the further conversion with alkali metal hydrides--an optically active lactone of the formula: ##STR5## as an optically active intermediate product. A significant drawback for an industrial use of such process consists in the use of the expensive optically active compounds chloresterol and ephedrine as well as expensive alkali metal hydrides. The processes of European Published Patent Applications Nos. 0161580 and 0173185 are tainted with the same drawback, namely the use of expensive optically active compounds.